1. Technical Field
The present invention relates to a brake system adapted for use in a vehicle, and particularly to a brake system for applying a brake force to the power transmission line of the vehicle.
2. Background Art
Generally, a large amount of heat exchange takes place in braking large vehicles such as a large bus or truck, and usually such vehicles are equipped with an auxiliary brake system in addition to a main brake system (foot brake). In one type of the auxiliary brake system, such as an exhaust brake, the auxiliary brake system produces a force which is directed from the vehicle wheels toward the engine of the vehicle. The crankshaft of the engine is rotated by such a force, and thereby the engine is decelerated. In another type, a rotor is provided in a propeller shaft of the vehicle, which consumes energy from the engine when it is rotated by the engine so that the rotor applies brake force to the engine.
FIG. 4 illustrates an example of the auxiliary brake system of the latter type, which is generally called an "electrical retarder." The electrical retarder b has a casing, electromagnets and a rotor housed in the casing. An eddy current (Foucault current) is produced when the rotor rotates between the electromagnets, i.e., when the rotor rotates in the magnetic field. The electrical retarder b expels the eddy current (Foucault current) in the form of ohmic heat. It is advantageous to provide this brake system b between the propeller shafts a of the vehicle, since the electrical retarder b serves as a center bearing of the propeller shafts a. However, the rotor requires cooling since the electrical retarder generates a considerable amount of heat. A cooling device raises the cost of the auxiliary brake system and makes the arrangement complicated.
On the other hand, the assignee of the present invention developed another type of auxiliary brake system, namely a turbo compound engine which is disclosed in Japanese Patent Application No. 61-22817 (Laid Open No. 63-85222 (1989)). This patent application also teaches an arrangement employing a rotor. However, the rotor in this case is provided in the exhaust line of the engine and serves as an energy recovering element in one mode and a brake force producing element in the other mode. Also, it produces a brake force mechanically. The shortcoming of this arrangement is that a complicated mechanism for switching the function of the rotor is necessary.